The purpose of this research is to develop clinically useful procedures for the cryopreservation of platelets and granulocytes. A major obstacle to the preservation of these two cell types has been the introduction of sufficient concentrations of cryoprotectant to achieve a good recovery of functioning cells. Past investigations have generally failed to appreciate the osmotic stresses inherent in the addition and removal of cryoprotectants. In this study we will establish in advance both the limits of osmotic tolerance and the transmembrane flux rate for the cryoprotective agent. This will permit the design of introduction and removal protocols that will not exceed the osmotic tolerance of the cells. This is particularly important for granulocytes which appear to have limited tolerance to hyperosmolality. The second problem arises when osmotic tolerances are carefully observed, since the addition of cryoprotective solutions sufficiently dilute to avoid osmotic stress leads to samples of unwieldy volume. A critical component of this proposal is the use of either the cross-flow filtration technique of dialysis to permit the addition and removal of cryoprotectant while maintaining a constant specimen volume. We believe that the mechanisms of freezing injury and cryopreservation are now sufficiently understood so that a logical approach to cryopreservation is possible and that procedures can be developed for both platelets and granulocytes that will lead to a high percentage recovery of clinically effective cells. New developments in the treatment of the leukemias and the increasing use of high-dose chemotherapy for a variety of reasons is creating an increasing need for the preservation of autologous cells and for large quantities of matched, single-donor, allogeneic preparations. Such applications will be possible only through the use of cryopreservation.